Method and apparatus for increasing the ductility of an article during a forming operation



Dec. 19, 1967 C JR 3,358,488

METHOD AND APPARATUS FOR INCREASING THE DUCTILI'I'Y OF AN ARTICLE DURING A FORMING OPERATION Filed June 5, 1965 2 Sheets-Sheet l u] 76 2 1111110! I I I I I III," 1 II lIIIIIIIl/IIIIIIII/IIlIl/IT 4 WAY VALVE PRESSURE- '18 REGULATOR CO NT R0 LLE INVENTOR E J. F UCHS, JR.

ATTORNEY Dec. 19, 1967 F. J. FUCHS, JR 3,358,488

METHOD AND APPARATUS FOR INC FASING THE DUCTILITY OF AN ARTICLE DURING A FORMING OPERATION Flled June 3, 1965 2 Sheets-Sheet 2 57 INVENTOR, 1-? J. Fae/7's, JR.

BY A? K ATTORNEY United States Patent ()fifice 3,358,488 Patented Dec. 19, 1967 3,358,488 METHOD AND APPARATUS FOR INCREASING THE DUCTILITY OF AN ARTICLE DURING A FORMING OPERATION Francis J. Fuchs, Jr., Princeton Junction, N.J., assignor to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Filed June 3, 1965, Ser. No. 461,121 17 Claims. (Cl. 7262) ABSTRACT OF THE DISCLOSURE The expansion of a tube to an enlarged diameter by applying fluid pressure to the interior and exterior of the tube sufficiently great to render the tube more ductile, and increasing the interior fluid pressure while relieving the exterior fluid pressure, to expand the more ductile tube and maintain the tube more ductile during the expansion.

This invention relates to a method and apparatus for increasing the ductility of an article during a forming operation and more particularly to a method of and apparatus for applying hydrostatic forces to the exterior and interior of an article to increase its capacity to deform while maintaining a differential between the forces to deform the article without fracture.

In commercial practice, tubes made from materials such as copper, brass, bronze, aluminum, mild steel and other low strength materials are expanded by subjecting the interior of the tube to high fluid forces to expand the tube or a portion thereof outwardly to a cylindrical die. However, generally the tube diameter can only be increased 30% during the expansion process before the tube material either fractures or unevenly thins out in localized areas. Furthermore, it is extremely diflicult, if not virtually impcxssible, to expand tubes made from hard-to-form materials such as molybdenum, and high strength steels.

Experiments have established that tensile specimens made from a variety of metals and other plastic material exhibit a phenomena of greatly increased capacity for deformation or increased ductility when the tensile specimens are subjected to high hydrostatic forces during tensile tests. These experiments have been documented in a book by Mr. P. .W. Bridgman entitled, Large Plastic Flow and Fracture published by McGraw-Hill Book Company of New York in 1952.

Accordingly, an object of this invention is to provide a new and improved method of and apparatus for increasing the ductility of an article during a forming operation.

An additional object of this invention is to provide a method of and apparatus for applying hydrostatic forces of suflicient magnitude to opposite sides of an article to increase its capacity to deform while maintaining a force differential to eflectuate a deformation of the article without setting up detrimental stress concentrations.

An additional object of this invention is to providea method of and apparatus for applying opposing forces to render a tube ductile and then subjecting the tube to bydraulic and mechanical forces to expand and longitudinally deform the ductile tube while maintaining a uniform wall thickness.

Another object of this invention resides in the utilization of an elastic expansion of a forming die to bleed high pressure fluid from a die cavity during a hydraulic forming operation to provide a force difierential which is effective to deform an article positioned within the forming die.

With these and other objects in view, the present invention contemplates a method of and apparatus for subjecting an article to opposing hydraulic forces to render the article more ductile, while maintaining a force differential to deform the article. More particularly, in practicing the invention a force of suflicient magnitude is applied to a fluid in the interior of a tube to expand the tube outwardly to pressurize fluid trapped between the tube and the walls of a die whereupon a reactive hydrostatic force is exerted on the exterior of the tube to render the tube ductile. The interior force is then increased to further expand the now ductile tube. The trapped fluid is bled by the expansion of a die housing when the pressure of the trapped fluid on the exterior is above a predetermined pressure needed for continuing the tube expansion. Simultaneously with the expansion of the tube, mechanical longitudinal forces are applied to compress the tube lengthwise to maintain a uniform tube wall thickness.

These and other objects and advantages of the present invention will be apparent by reference to the following detailed description and the accompanying drawings, in which:

FIG. 1 is a side elevational view of a tubular member to be formed by the method and apparatus of the present invention;

FIG. 2 is a longitudinal cross-sectional view of the tube shown in FIG. 1 after being formed;

FIG. 3 is a front elevational view, partly cut away, of a forming press embodying the principles of the invention showing a die assembly and hydraulic systems for moving upper and lower rams against the die assembly;

FIG, 4 is a cross-sectional view of the die assembly illustrating the unformed tube in relation to forming members in the die assembly; and

FIG. 5 is a view similar to FIG. 4 showing the formed tube in relation to the forming members.

Referring to FIG. 1, there is shown an article such as a tubular member 10 that may be formed, expanded, bulged or enlarged by the method and apparatus of the present invention. This tubular member is constructed of a material such as copper, brass, aluminum, molybdenum, or steels that will exhibit a substantial increase in ductility when subjected to high hydrostatic pressures. As shown in FIG. 2, the formed tube 10 has an end section 11, a first radius 12, a first intermediate expanded section 13, a second radius 14, a second intermediate expanded section 15, a third radius 16 and an end section 17 During the forming operation the length of the expanded tube 10 is decreased from its original length but the expanded tube 10 has a uniform tube wall thickness. For example, a copper tube having an inside diameter of 0.376 inch and a length of 8.33 inches is expanded to form a first intermediate expanded section having an inside diameter of 0.505 inch and a second intermediate expanded section having an inside diameter of 0.756 inch. The length :of thecopper tube is decreased from 8.33 inches to 6.25

-of the press. The die assembly 18 is supported by a horizontal support member 21 which is rigidly attached to a bed. 22 of the forming press. The support member 21 has a vertical aperture 23 therethrough in alignment with the vertical axis of the press.

- A cam 24 is connectedto the upper ram 19. The cam 24 has three distinct contoured surfaces, designated as letters A, B, and C. The cam 24 engages a cam follower 25 which is responsive to the contour of the cam surface when the cam 24 is moved in the vertical direction with the upper ram 19. The cam follower 25 actuates'a pressure controller 26 which in turn controls the hydraulic fluid pressure applied to the lower ram 20. A 4-way valve 27 is .connected in the hydraulic lines between the pressure controller 26 and the lower ram 20 to change the direction of hydraulic fluid flow to the lower ram 20 for raising or lowering the lower ram 20. The movement of the upper ram 19 is responsive to hydraulic fluid pressure regulated by a pressure regulator 28 and a 4-way valve 29.

As shown in FIG. 4, the die assembly 18 comprises a booster or a stationary cylinder 31 that is mounted vertically on the support member 21. The booster 31 has a bore 32 therethrough and a counterbore 33 in the lower end thereof. The upper end of the cylinder 31 has a reduced diameter section 34 forming a stepped abutment 36. A piston 37 is slidably mounted in the counterbore 33 and projects through the aperture 23 of the support member 21 to engage the lower ram 20.

A hollow cylindrical first forming member or first die 41 is slidably mounted over the reduced diameter section 34 of the booster 21 to engage the abutment 36. The first forming member 41 has a cylindrical-shaped die recess 42 in the upper end thereof for forming the first radius 12 and the first intermediate expanded section 13 of the tube 10. The first forming member 41 also has an arcuate upper end die surface 43 for forming the second radius 14 on the tube 10.

A hollow mandrel 46 for supporting a tube thereon is positioned inside the first forming member 41 and is'sllpported therein by the reduced diameter section 34 of the booster 31. The lower end ofthe mandrel 46 has a flange 47 for engaging one end of the tube 10. The mandrel 46 has a plurality of radial apertures 48 for communicating 'fluid from the interior of said mandrel to the interior of the tube 10.

A movable cylindrical die housing 51 has a bore 52 therethrough and a conical counterbore 53 in the upper end thereof forming a shoulder 54 With'thC bore 52. The conical shape of the counterbore facilitate the removal of the formed tube 10. The lower end of the housing 51 is .slidably mounted over the first forming member 41. The

cylindrical housing 51 will elastically expand radially when subject to sufiicient interior fluid forces above'that necessary to render-ductile'the materialof the'tube 10.

A hollow secondforming member frustum-shaped or split die'bushing 56 for forming theexpanded tube section 15 is mounted in the conical counterbore 53 engaging shoulder 54. A frustum-shapedthird forming member 61 is loosely mounted in the counterbore 53. The forming member 61 has an arcuate end surface 62 for forming the third expanded tube radius 16. In addition, the third forming member 61 has'a bore 63 extending'therein for slidably receiving and supporting the other end of the mandrel 46. A counterbore 64 is formed in the third forming member 61-forming a shoulder '66 for supporting and engaging the .end 17 of the tube .10. The housing 51 and the second and third forming members '56 and 61 define a second die 67. p

A frustum-shaped plug 71 is positioned in the upper end of the conical counterbore 53 and extends partly therefrom to enclose the upper nuclei the counterbore 53 and'to limit the movement of the second and .third forming members 56 and 61 in the counterbore 53.

As shown in FIGS. 4 and Sfthe formingmembers 41 56, and 61 deflnega die cavity 72 into which the intermediate tube sections are expanded and formed. The die cavity 72 and the booster 31 and mandrel 46 are filled with forming fluid.

A pressure plate 73 is mounted on the plug 71 and is attached to the upper end of the housing 51 bycountersunk bolts 74. The bolts 74 pass through the plate 73 and into the housing 51 to force the pressure plate 73 against the plug 71 to 'slidably move .the plug 71 downwardly into a press fit with the housing 71. The degree of press fit may be varied by the torque applied to the bolts 74.

when expanding a copper tube, sufficient 74 to move the plug 71 into the housing 51; that 'is, the

For example, torque is applied to the bolts a 0.003-inch press fit with diameters of the conical counterthe housing 51 will than the corresponding bore 53. During the forming operation, elastically expand from the 0.003-inch press fit with the plug 71 when the fluid pressure in the cavity 72 exceeds a value such as 86,300 psi, to bleed the fluid from the cavity 72. Thus, the variable degree of press fit of the plug 71 with the housing 51 provides a means of determining the pressure at which the fluid will bleed from the cavity 72 during the forming operation.

Radial grooves 76 are formed in the lower surface of the plate 73 for communicating fluid bled'from the cavity 72 to the exterior of the die assembly 18.

In use of the forming apparatus, a tubular blank 10 is placed on the mandrel 46 with end 11 engaging the flange 47. Then the mandrel 46 and tube are inserted into the first forming member 41 so that the flange 47 engages the reduced diameter section 34 of the booster 31. The housing 51'is positioned over the first forming member 41 and then the forming fluid is poured into the housing 51. The second forming member '56 is then inserted into t .e counterbore 53 to engage the shoulder 54, The third forming member 61 is inserted into the counterbore 53 so that the upper end of the mandrel 46 slides into the bore 63 and the end 17 of the tube 10' slides into the counterbore 64 and engages shoulder 66 leaving a gap 77 between the third forming member '61 and the second forming member 56.

Next, the plug 71 is then inserted into the counterbore 53. The pressure plate is subsequently positioned on'the plug 71 and screwed to the housing 51 forcing the plug 71 downwardly into a predetermined press fit with the housing 51.

The pressure regulator 28. and valve 29 are initially operated to lower the upper ram 19 to engage the pressure plate 73. As the ram is initially lowered, the cam surface A move into engagement with the cam follower 25 to actuate the pressure controller 26 to increase the pressure of the hydraulic fluid The 4-way valve 27 is then actuated to impress the hydraulic pressure upon the lower ram 20 to move piston 37 upwardly. As the piston is moved upwardly, it compresses the fluid in the booster 31 and mandrel 46 which exerts a hydrostatic force through the'apertures '48 to the tube interior to initially expand the intermediate tube sections outwardly subjecting the tube material to tanv gential stresses (hoop-tensile stresses). As the tube is initially expanded, the

fluid enclosed in the die cavity '72 is compressed to exert a back or reactive hydrostatic force of sufficient magnitude to substantially increase the ductility of the tube 10.

The pressure regulator 28 and valve 29 are again operated to move the upper ram 19 against the pressure plate 73 to telescope the die assembly 18 by slidably-moving the housing 51 on the stationary first forming member '41.

As the die assembly is telescoped, third forming member 61 is moved toward the first forming member 41 to compress the die cavity 72 to further increase the fluid pressure in the cavity 72. Also, as the upper ram moves downwardly, 66 moves against the tube to longitudinally compress the tube material between tube sections in the cavity 72 to increase the fluid pressure the cam surface V engages the cam follower 25 causing the pressure-controller to provide an increasing hydraulic pressure to the lower ram20 to increase the fluid pressure on the tube interior to further expand the intermediate tube sections in the cavity 72 to increase the fluid'pressure going to the lower .ram 20.

the third forming member shoulder V the shoulder 66 and the mandrel flange 47 to maintain a uniform wall thickness during the expanded housing counterbore 53 and through the plate grooves 76 t0 the exterior of the die assembly 18. The bleeding of the fluid from the cavity enables the intermediate tube section to further expand in the cavity 72.

The fluid pressure in the cavity 72 exerts a force on the interior of the first forming member 41 to elastically expand the first forming member 41 against the housing 51 forming a seal to prevent fluid bleeding between the housing 51 and the first forming member 41.

As the upper ram 19 descends further, cam surface C engages the cam follower 25 to accelerate the pressure build-up in the interior of the tube to make sure that the fluid in the cavity 72 is completely bled from the cavity 72 to properly form the tube against the forming members, particularly the second tube radius 13 and the third tube radius 15.

After the tube It? has been formed, the 4-way valve 29 is actuated to raise the upper ram 19 from the pressure plate 73. At the same time, the 4-Way valve 27 is actuated to lower the ram 29. The pressure plate 73 is now removed from the housing 51 allowing the plug 71 to slide or back out of the press fit with the conical-shaped wall of the counterbore 53. Subsequently, the plug 71, the third forming member 61, the tube 10, the mandrel 46, and the second forming member 56 are removed from the housing 51. The formed bulged tube 10 is then removed from the mandrel 46.

It is to be understood that the above-described embodiments are simply illustrative of the principles of the invention. Numerous other modifications may be devised without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of enlarging the diameter of a tube While maintaining a uniform Wall thickness, which comprises the steps of:

applying fluid pressure of sufficient magnitude to the interior and exterior of said tube for rendering said tube ductile, increasing the fluid pressure on said tube interior for enlarging the diameter of the then ductile tube, and

applying a force during said diameter enlargement to one end of said then ductile tube for longitudinally compressing the material of said tube to maintain a uniform wall thickness.

2. A method of expanding a tube in a fluid filled die cavity in which the tube is composed of a material that is rendered more ductile upon subjection to high fluid forces, which comprises the steps of:

applying an increasing pressure to fluid inside of said tube for expanding said tube outwardly to increasingly pressurize the fluid in said cavity to exert a high reactive fluid force to the exterior of said tube to render said tube ductile, and

relieving the increasing pressure on the exterior of said tube to render said interior pressure eflective to expand said tube. 3. A method of expanding a section of a tube within a fluid filled die having a cavity therein for receiving said section, said tube composed of a material that is rendered more ductile upon subjection to predetermined fluid forces, which comprises the steps of:

applying a force of suflicient magnitude to the fluid in the interior of said tube for expanding said tube into said cavity to pressurize the fluid in said cavity to exert a fluid force on the exterior of said tube to render said tube ductile, increasing the force on said interior fluid for further expanding the then ductile tube section in said cavity, and bleeding the fluid from said cavity when the pressure in said cavity is above a predetermined value while maintaining said tube ductile and containing said tube section expansion. 4. A method of forming a bulge in a tube constructed 6 of material that is rendered more ductile upon subjection to predetermined opposed compressive forces,

mounting the tube within a pair of telescoping dies imparting relative movement between said dies to compress the fluid to impart a compressive force on the exterior of said tube, impressing fluid to the interior of said tube at a pressure which increases with the relative movement to sequentially subject said tube to said predetermined compressive forces and then to a pressure diflerential to bulge said tube against the walls of said dies, and

applying longitudinal forces to walls of said tube to maintain the thickness of said walls constant during said bulging.

5. A method of expanding the diameter of a tube While maintaining a uniform wall thickness, which comprises the steps of:

placing said tube Within a fluid filled forming die having a diameter greater than said tube to form a die cavity between said die and said tube,

applying fluid pressures of sufiicient magnitude to the interior and exterior of said tube for rendering said metal tube ductile, increasing the fluid pressure of said interior to force and expand the then ductile tube outwardly,

simultaneously bleeding the fluid from said cavity as said tube is expanded into said cavity to mantain a pressure differential which is of suflicient magnitude to continue the expansion of said tube, and

applying longitudinal forces during said expansion to said tube to longitudinally deform the then ductile tube to maintain a uniform Wall thickness.

6. A method of expanding a section of a tube while 0 maintaining a uniform wall thickness, said tube composed of a material that is rendered more ductile upon subjection to predetermined fluid forces, which comprises the steps of:

placing said tube within a fluid filled die having a cavity therein for receiving said tube section, applying a force of suflicient magnitude to the fluid in the interior of said tube to expand said tube section into said cavity to pressurize the fluid in said cavity to exert a predetermined reactive fluid force on the exterior of said tube to render said tube ductile, increasing the force to said interior fluid to further expand the then ductile tube section in said cavity, simultaneously compressing said tube lengthwise for deforming the then ductile tube to maintain a uniform wall thickness, and bleeding the fluid from said cavity as said tube is expanded when the fluid pressure in said cavity exceeds a predetermined magnitude to maintain said tube ductile and to continue the expansion of said tube. 7. In a forming apparatus for expanding the diameter of a tube composed of a material that is rendered more ductile upon subjection to predetermined forces,

a die for receiving fluid and for supporting said tube in said fluid, means for applying an increasing force to said fluid to pressurize said fluid to exert interior and exterior pressures of suflicient magnitude to render said tube ductile, and means responsive to the increasing pressure on the exterior of said tube for relieving said exterior pressure to render said interior pressure eflective to expand said tube while said tube is maintained in a ductile state. 8. In a forming apparatus for expanding the diameter of a tube composed of a material that is rendered more ductile upon subjection to predetermined fluid forces;

a die for receiving fluid and for supporting said tube in said fluid, means for applying an increasing force to the fluid in the interior of said tube to expand said tube outof a tube while maintaining a wardly to increasingly pressurize the fluid on the exterior of said tube to exert a sufficient reactive fluid force on said exterior to render said tube ductile, and

means responsive to a redetermined pressure of the fluid on the exterior of the tube for relieving the increasing pressure on said exterior to render said interior force effective to further expand said tube while said tube is maintained in a ductile state.

9. In a forming apparatus for expanding the diameter uniform wall thickness, said tube composed of a material that is rendered ductile upon subjection to predetermined fluid forces;

a hollow die assembly for receiving fluid and for supporting the tube within a cavity between said tube and the outer wall of said die assembly,

means engaging one end of said tube for longitudinally compressing the material of said tube,

means responsive to said compressing means for applying an increasing fluid force to the interior of said tube to expand said tube outwardly to maintain a uniform tube Wall thickness and to increasingly pressurize the fluid in said cavity to exert a fluid force to the exterior of said tube to render said tube ductile, and

a plug press fitted Within one end of said die assembly from which the assembly moves for relieving the increasing pressure on said exterior to render said interior force effective to further expand said tube while said tube is maintained in a ductile state.

10. In an apparatus for forming a bulge in a tube constructed of material Whose ductility is increased upon subjection to predetermined compressive pressures,

a first die having a die cavity for receiving fluid,

a second die slidably mounted on said first die,

a mandrel for supporting a tube within said first and second dies, said mandrel having passageways therethrough communicating with the interior of said tube,

means for imparting a relative movement between said first and second dies to pressurize the fluid to exert a pressure on the outside of said tube,

means for impressing pressurized fluid through the mandrel passageway to expand the tube and subject it to said predetermined compressive pressures to render said tube ductile,

means actuated by the relative movement of said dies for applying longitudinal compressive forces to said tube to maintain the tube wall thickness constant during expansion, and

means responsive to said relative movement of said dies for increasing the pressure on the fluid passing to said mandrel passageway to further increase the pressure differential and continue the tube expansion into engagement with the walls of said first and second dies.

11. In an apparatus for forming a bulge in a tube constructed 'of metal that is rendered more ductile upon subjection to predetermined opposing pressures,

means having a ing said tube,

a cylindrical die surrounding said supporting means and having a die surface spaced from said tube for receiving fluid,

a hollow die housing slidably mounted on said cylindical die and having a conical recess,

a conicalplug force fitted into said conical recess,

means for moving said die housing to apply compressive forces to said fluid to exert forces on the exterior of said tube,

means for supplying pressurized fluid through said pacsage'way to oppose s'ai'd exterior forces and expand said tube, and v means actuated by the moving means for increasing the pressure on the fluid inside said tube to apply pressure through said exterior fluid to expand s'aid hollow passageway therethrough for supportdie housing from said plug to relieve the pressure on said exterior fluid to increase the pressure differential and further expand the tube into engagement with said die surface of said cylindrical die.

12. In a die apparatus for expanding a tube constructed of material that is rendered ductile upon application of opposed compressive forces,

a hollow cylindrical first forming member for receiving fluid and for supporting one end of said tube,

a hollow cylindrical housing, slidably mounted over said first forming member, said housing having an internal recess therein,

a hollow second forming member positioned in said housing recess,

a third forming member juxtaposed said second forming member in said recess for supporting the other and of said tube, V V

a plug press fitted in said housing recess for enclosing said recess,

means including an adjustable pressure controller for applying compressed fluid to the interior of said tube,

means for moving the die housing to apply compressive forces to the fluid to render the tube ductile, and

means actuated by the moving means for adjusting the pressure controlled to increase the pressure of the fluid inside the tube to expand the tube to compress the exterior fluid and move the die housing from the press fitted plug whereupon the exterior fluid is bled and the tube expands into engagement with the first, second, and third forming members.

13. In a forming die apparatus for expanding a tube constructed of material that is rendered ductile upon application of opposed compressive forces,

a movable cylindrical die housing through and a conical counterbore in one end thereof forming a shoulder with said bore,

a stationary cylindrical first forming member for receiving fluid and mounted in the other end of said die housing for enclosing said other end of said housing and engaging one end of said tube,

a hollow frustum-shaped second forming member positioned in said housing counterbore engaging said housing shoulder,

a frustum-shaped third forming member in juxtaposition to said second forming member in said housing counterbore for engaging the other end of said tube,

a frustum-shaped plug press fitted in said one end of said housing engaging said third forming member for enclosing said one end of said housing,

means including an adjustable pressure controller for applying compressed fluid to the interior of said tube,

means for moving the die housing to apply compressive forces to the fluid to render the tube ductile, and

means actuated by the moving means for adjusting the pressure controller to increase the pressure of the fluid inside the tube to expand the tube to compress the exterior fluid and move the die housing from the press fitted plug whereupon the exterior fluid is bled and the tube expands into engagement with the first,

second, and third forming members.

14. In a high pressure forming apparatus for expanding a tube while maintaining a uniform tube wall thickness, said tube composed of a material that is rendered ductile upon subjection to predetermined fluid forces;

'a stationary cylinder having a bore 'thereth'rough and a counterbore in one end of said cylinder, said cylinder having a reduced cylindrical other end forming an abutment therewith,

a piston slidably mounted in said cylinder counterbore,

a hollow mandrel having a flange engaging said reduced cylinder end for supporting said tube, said mandrel having a plurality of radial apertures for communicating fluid from the interior of said mandrel to the interior of said tube,

a hollow cylindrical first forming member having one having a bore thereend surrounding said cylinder recess and said mandrel flange and engaging said cylinder abutment,

an elastically expandable cylindrical housing having a bore therethrough which is slidably mounted on said first forming member, said housing having a conical counterbore to form a shoulder with said housing bore,

a hollow frustum-shaped second forming member mounted in said conical counterbore engaging said housing shoulder,

a frustum-shaped third forming member mounted in said conical counterbore, said third forming member having a stepped axial cavity therein for supporting and engaging the other end of said tube,

a frustum-shaped plug press fitted in said conical counterbore and engaging said third forming members,

a pressure plate positioned against said plug,

a ram engaging said pressure plate,

a contoured cam attached to said ram,

a hydraulic pressure control means responsive to the contour of said cam for controlling the pressure of fluid to be applied to move said piston in said stationary cylinder,

valving means for rendering the hydraulic pressure control means effective to move said piston in said stationary cylinder to pressurized fluid to be received in said cylinder and said mandrel to exert a suflicient hydrostatic force on the interior of said tube to expand said tube outwardly to pressurize fluid to be received between the tube exterior and the first, secnd, and third forming members to exert a hydrostatic force on the exterior of said tube to render said tube ductile, and

means for moving said ram (1) against said pressure plate to slidably move said cylindrical housing on said first forming member to move said third forming member to compress said tube material lengthwise between said mandrel and stop and third forming member and to further compress fluid to be received on the exterior of said tube and (2) to move said cam to actuate said hydraulic pressure control means to provide an increasing pressure to said tube interior to further expand said tube outwardly to further increase said exterior pressure to expand said housing from said plug to bleed the exterior fluid therebetween to continue the expansion of said tube.

15. A method of expanding a hollow tube to an enlarged diameter, comprising:

applying fluid pressure to the interior and exterior of the tube of magnitudes suflicient to render the tube more ductile; and

increasing the fluid pressure applied to the interior of the tube over the fluid pressure applied to the exterior of the tube by an amount suflicient to expand the more ductile tube to the enlarged diameter.

16. A method of expanding a hollow tube to an enlarged diameter, comprising:

simultaneously applying increasing fluid pressure to the interior and exterior of the tube of a magnitude sufficient to render the tube ductile,

establishing a predetermined pressure differential between the fluid pressure applied to the interior of the tube and the fluid pressure applied to the exterior of the tube sufficient to expand the more ductile tube to the enlarged diameter and to maintain the tube more ductile during expansion, and

applying a force to the more ductile tube during said expansion to compress the tube to control the tube Wall thickness.

17. A method of expanding a hollow tube to an enlarged diameter, comprising:

applying fluid pressure to the interior and exterior of the tube;

establishing a predetermined pressure differential between said applied fluid pressures suflicient to render the tube more ductile, to expand the more ductile tube to the enlarged diameter, and to maintain the tube more ductile during expansion; and

compressing the more ductile tu-be during expansion to provide the enlarged tube with a uniform wall thickness.

References Cited UNITED STATES PATENTS 633,430 9/1899 Crowden 7261 650,755 5/1900 Huber 7256 2,038,304 4/ 1936 Middler 72-3 67 X 2,902,962 9/ 1959 Garuin 7 2-23 3,072,085 1/1963 Landis 72-58 3,229,488 1/1-966 Smith 72-56 FOREIGN PATENTS 476,793 9/ 1951 Canada.

CHARLES W. LANHAM, Primary Examiner. K. C. DECKER, Assistant Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,358,488 December 19, 1967 Francis LT. Fuchs, Jr.

It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 36, for "facilitate" read facilitates column 4, line 16, after "tube" insert l0 line 37, for "move" read moves lines 64 and 65, for "sections in the cavity 72 to increase the fluid pressure the cam surface V" read expansion process. As the upper ram 19 descends, the cam surface B column 5, line 73, for "containing" read continuing column 6, line 25, for "of" read on line 28, for "mantain" read maintain column 7, line 65, for "cylindical" read cylindrical column 8, line 17, for "and" read end line 25, for "controlled" read controller line 40, after "and" insert for column 9, line 16, for "members" read member line 26, for "pressurized" read pressurize line 38, after "mandrel" strike out "and".

Signed and sealed this 11th day of February 1969.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

15. A METHOD OF EXPANDING A HOLLOW TUBE TO AN ENLARGED DIAMETER, COMPRISING: APPLYING FLUID PRESSURE TO THE INTERIOR AND EXTERIOR OF THE TUBE OF MAGNITUDES SUFFICIENT TO RENDER THE TUBE MORE DUCTILE; AND INCREASING THE FLUID PRESSURE APPLIED TO THE INTERIOR OF THE TUBE OVER THE FLUID PRESSURE APPLIED TO THE EXTERIOR OF THE TUBE BY AN AMOUNT SUFFICIENT TO EXPAND THE MORE DUCTILE TUBE TO THE ENLARGED DIAMETER. 